The present invention relates to a pneumatic horn. A pneumatic horn of the type under discussion comprises a housing portion, a base portion connected with the latter, a pipe connecting piece, which is arranged inside the housing portion, a sound horn, which is held in an opening of the housing portion and communicates with the pipe connecting piece, a compressed-air duct leading into the housing portion, and a diaphragm which is fixed between the housing portion and the base portion and is adjacent to the pipe connecting piece.
Pneumatic horns of this type are attached externally at the body structures or superstructures of trucks or ships and are operated with high air pressures up to 10 bar and more in order to produce horn sounds which can be heard from far away, wherein the tone pitch depends on the length of the air column formed by the sound horn, the working pressure, the diaphragm thickness and gripping and other parameters. The horn and the housing are constantly exposed to weather conditions and, accordingly, to corrosive stress.
In the pneumatic horn of this type, which is known from DE-OS No. 33 19 140, the outer rim of the sheet material base directly encompasses the outwardly canted circumferential rim of the sheet metal housing and is permanently fixed at the latter by means of inwardly flanged brackets, wherein the diaphragm is gripped between the two sheet metal portions. The tensioning of the diaphragm can be changed by means of stretched bulges of the sheet metal base. However, because of unavoidable manufacturing tolerances and irregularities in the connection of the sheet metal portions, this construction provides no uniform gripping of the diaphragm along the circumference and no satisfactory sound quality. It is also hardly possible to remove the sheet metal base in order to exchange the diaphragm without causing damage.
In addition, an automobile horn is known from DE-GM No. 1967 110, in which the housing portion and the base portion are thick-walled cast pieces which are detachably connected by means of threaded boreholes of the housing portion, which are arranged so as to be spaced along the circumference, and screws which can be screwed into the latter. This construction is not only very heavy and costly to manufacture, but there is also no uniform gripping of the diaphragm along the circumference. In order to achieve an appropriate appearance, costly aftertreatment and chroming of the cast pieces is required, although this will begin to chip off sooner or later, which considerably impairs the appearance of the compressed-air flow.